NMR study of heterogeneity in pyridine-N-oxide...HCl crystal

• Authors: Vytautas Balevicius , Alexandar Gacesa , Janez Plavec
• Languages of publication: EN

Abstracts

EN

An origin of narrow 1H NMR signals in pyridine-N-oxide (PyO)...HCl crystal has been investigated by means of MAS, SPEDAS, NOESY and COSY techniques. Spectra of crystalline samples are compared with those of solid phase obtained from liquid PyO...HCl solutions (in acetonitile/H2O) after the heterogeneous phase separation. It has been concluded that partially resolved peaks in 1H NMR spectra of solids are related with heterogeneity of spin system and presence of different H-bond clusters of water molecules. NOESY spectra show no cross-peaks even at very long mixing time (500 ms). This indicates there is no exchange process between spins causing different peaks, and thus the corresponding molecular aggregates are captured in “islands of mobility8 without any channels sufficient for exchange. Appearance of MAS side bands as “pseudo8 cross-peaks in 2D NMR spectra using MAS/COSY technique is reported. In the case of accidental coincidence of spinning frequency (ωMAS) with spectral distances between some diagonal signals, intensive non-diagonal peaks are observed at the corresponding cross-positions. A misleading conclusion concerning spin coupling is easy to avoid using various ωMAS.

Keywords

EN

NMR spectroscopy; phase transitions; hydrogen bonding; pyridine-N-oxide; 82.56.-b; 64.70.-p; 33.15.Fm

• Publisher: De Gruyter Open
• Journal: Open Physics
• Year: 2004
• Volume: 2
• Issue: 1
• Pages: 120-131

Dates

published

1 - 3 - 2004

online

1 - 3 - 2004

Contributors

author

Vytautas Balevicius

• Faculty of Physics, Vilnius University, Saulëtekio 9, LT-2040, Vilnius, Lithuania

author

Alexandar Gacesa

• Slovenian NMR Centre, National Institute of Chemistry, SI-1000, Ljubljana, Slovenia

author

Janez Plavec

• Slovenian NMR Centre, National Institute of Chemistry, SI-1000, Ljubljana, Slovenia

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Identifiers

DOI

10.2478/BF02476276